Engine build prep (2014)

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Fast Eddie said:
Well, I got back home from a couple of weeks working in India (it ain't half hot Mum!) and today I got chance of a few hours in the workshop...

I nailed the head on last time, but still had a lot of stuff to attach, set, tighten etc. everything seemed to go together nicely though.
Top end all nailed and tightened now:

Engine build prep (2014)


Engine build prep (2014)
Click to expand...

I am wondering about the rocker feed extension on your oil line? I have a Comnoz headsteady, and when I put my bike back together I have a new Venhill SS line that I will be using with drilled out rocker spindles. So, is the extension to give better clearance with the headsteady, or something else?
 
Gortnipper: The rocker feed in the pics is as it was supplied, its from RGM and is good kit. It looks a little longer than needed because of how I have routed it I guess. I am also going to change my rocker spindles for drilled through ones and this will allow me to greatly simplify this plumbing.

850commando: The air filter is a Pipercross foam filter. I used it because I want to use velocity stacks. I tried the stacks last year and they made a few BHP difference on the dyno. So, I now run the velocity stacks inside the foam filter. The filter I used is this one:
http://www.ebay.co.uk/itm/PX-air-filter ... 1036462453
 
What do the velocity stacks do to the power curve? Do you lose any at the bottom end?
 
Onder said:
What do the velocity stacks do to the power curve? Do you lose any at the bottom end?
Click to expand...

They don't exactly transform the output, but they do make a small difference. As with other old Brit motors I have experimented with, short stacks turned out better. Here's the figures comparing velocity stacks to the stock Kehein inlet stub:

With 70mm long velocity stacks: Power +1.4 bhp. Torque -2.9 ft/lbs

With 40mm long velocity stacks: Power +1.8 bhp. Torque +0.3 ft/lbs

Bear in mind these tests were done with 35mm FCRs and a JS1 cam all feeding a stock head, which would have basically been the 'bottleneck' in the system. The head has since been ported by Sir Comnoz and has 3mm oversize inlet valves as well, I therefore strongly suspect that if I were to repeat the test today, the overall benefit seen from using velocity stacks would be somewhat greater.
 
Hi guys,
I have been looking all over the net for the "Diamondyze" piston treatment and keep running into dead ends. The manufacturer only sells to dealers and the dealers seem to have broken links to their sites. Any help?
Thanks, Dan.
 
Fast Eddie said:
Onder said:
What do the velocity stacks do to the power curve? Do you lose any at the bottom end?
Click to expand...

They don't exactly transform the output, but they do make a small difference. As with other old Brit motors I have experimented with, short stacks turned out better. Here's the figures comparing velocity stacks to the stock Kehein inlet stub:

With 70mm long velocity stacks: Power +1.4 bhp. Torque -2.9 ft/lbs

With 40mm long velocity stacks: Power +1.8 bhp. Torque +0.3 ft/lbs

Bear in mind these tests were done with 35mm FCRs and a JS1 cam all feeding a stock head, which would have basically been the 'bottleneck' in the system. The head has since been ported by Sir Comnoz and has 3mm oversize inlet valves as well, I therefore strongly suspect that if I were to repeat the test today, the overall benefit seen from using velocity stacks would be somewhat greater.
Click to expand...



This is a friendly reminder to let you know that you are due for a dyno check-up. If the dyno check-up has been done, please post the results and ignore this reminder.

Glen
 
worntorn said:
Fast Eddie said:
Onder said:
What do the velocity stacks do to the power curve? Do you lose any at the bottom end?
Click to expand...

They don't exactly transform the output, but they do make a small difference. As with other old Brit motors I have experimented with, short stacks turned out better. Here's the figures comparing velocity stacks to the stock Kehein inlet stub:

With 70mm long velocity stacks: Power +1.4 bhp. Torque -2.9 ft/lbs

With 40mm long velocity stacks: Power +1.8 bhp. Torque +0.3 ft/lbs

Bear in mind these tests were done with 35mm FCRs and a JS1 cam all feeding a stock head, which would have basically been the 'bottleneck' in the system. The head has since been ported by Sir Comnoz and has 3mm oversize inlet valves as well, I therefore strongly suspect that if I were to repeat the test today, the overall benefit seen from using velocity stacks would be somewhat greater.
Click to expand...



This is a friendly reminder to let you know that you are due for a dyno check-up. If the dyno check-up has been done, please post the results and ignore this reminder.

Glen
Click to expand...


Please be aware that this automatic reminder will continue to appear until said check up has been performed. Thank you for your co-operation. Sincerely the Dyno-Police :shock:
 
Don't panic boys, Dyno check up will come!

It will take a bit longer than I'd hoped though cos I'm so busy with work these days and am away from home a lot, so I have to be a tad mindful not to arrive home, say hi to the family, and spend all my 'home time' in the shed / on the bike!

I've only managed to put 70 miles on it since getting it back together, and given the piston damage I seemed to cause last time around, I'm being a bit more careful this time.

It starts first or second kick, sounds as nice as ever, heck it even ticks over!

Strange as it feels to actually say this out loud... I am quite enjoying breaking it in... I think I had forgotten that the throttle has more than two positions...!
 
Guilty as charged.

My most humble apologies gents, a very hectic work schedule has made this much more delayed than anticipated.

I've only managed to put a few hundred road miles on the damned thing since nailing it back together, and I want to be sure its properly run-in this time.

I have started opening it up and have given it the odd squirt to 7,000.

My impression is that there is noticeably more pull around 3,500 to 4,500. Two or three times I have thought "Hey this is pulling well in third" only to find I was already in fourth! Its difficult to detect any noticeable increase in outright peak power though.

I hope to get it on the Dyno at the end of September.
 
Extra midrange would be very desirable. The (standard) Commando 850 is all about strong midrange, so an enhancement there will only increase the fun level.
One of my fears in messing with my stock bike is that the midrange will suffer in order to gain a few more peak hp. Even with a few more peak HP, the Commando is pretty flacid compared with similar displacement modern bikes. On the other hand, it does better than many moderns when it comes to low and midrange grunt.

Glen
 
I've not put may miles on a stock 850 Glen so am no expert. My own bike had a single Mikuni, K&N filter and peashooters fitted when I bought it. All things that folk say improve the low end torque at the expense of top end... But all I can say is that I certainly have not experienced any loss of bottom end torque.

But what is 'low end torque' ? I think that people's own comments about 'low end torque' ... 'Mid range' ... 'Top end power' is all relative. With the Mikuni fitted, mine ran out of breath at 5,000 rpm, which is firmly mid range in my book, now it pulls from 5,000 to over 7,000 stronger than it did from 1,000 to 5,000 before!

These findings were further supported when a mate with his mkIII and I rode back to back and swapped bikes last year. His bike felt so flat when doing roll on acceleration and mine just left it for dead, whichever of us was riding.

WTF am I waffling on about? I'm not entirely sure, but I guess my point is that despite many warnings against using bigger cams, bigger carbs and higher CR, the predicted downside has not materialised. The bike flies and its just a hoot to ride. I know it's a pussy compared to a R1 etc, and one has to draw the line somewhere, but to those who say 'what's the point in tuning an old bike' all I can say is try one out, it is SO MUCH more fun !!
 
Nigel, I'm sure it is a goer.
My quandry with the hop up idea started when Roger at RGM told me that most who converted to 920 kits "slowed the bike down" That put my 920 plans on hold.
I know you've gone a different route with the hop up and it's worked really well, but running out of breath at 5 k makes me think you weren't starting with a full on Commando. I'm guessing the single Carb really held it back.

I need to keep a close eye on the tach of my nearly stock MK3 or it will run right by 7 k rpm in first and second. It will also pull to 7 k in third and will pull 6700 in fourth, 21 tooth CS.

I do have an RH10 head in the drawer waiting in the drawer tho..........

Glen
 
worntorn said:
Nigel, I'm sure it is a goer.
My quandry with the hop up idea started when Roger at RGM told me that most who converted to 920 kits "slowed the bike down" That put my 920 plans on hold.
I know you've gone a different route with the hop up and it's worked really well, but running out of breath at 5 k makes me think you weren't starting with a full on Commando. I'm guessing the single Carb really held it back.

I need to keep a close eye on the tach of my nearly stock MK3 or it will run right by 7 k rpm in first and second. It will also pull to 7 k in third and will pull 6700 in fourth, 21 tooth CS.

I do have an RH10 head in the drawer waiting in the drawer tho..........

Glen
Click to expand...

I think a lot of early / older 920 kits used inappropriate, heavy, pistons and pins, out of a Ford I believe. And I'm guessing a lot of DIY builders didn't get cams, ports n carbs correct either.

My mates mkIII with stock twin Amals, would also rev out to 7000 in lower gears surprisingly easily. But mine had still gone by then!

My opinion is that the raise CR makes a big difference, but as I did so much at once, its impossible to tell what did what!

So, you got a RH10 sitting in the drawer eh? Now I know why you're keen to know the Dyno results of my head job! The smaller ports should equal greater velocity and greater low down pull Glen... Skim the barrel / head 0.040" whilst its down and Bingo...!

End Sept, all being well, I'll have it on the Dyno...
 
Ok Glen, your nagging has worked...

Dyno day is booked for Tue 27h Sept.

It will be interesting to compare objective Dyno figures with my seat of the pants conclusions.

My seat of the pants conclusions thus far, are:

1. Definite improvement in low speed running, smoother acceleration from idle and riding trough traffic etc. this is in quite some contrast with what we are led to expect from big cams, big carbs, big pistons, etc!

2. There is a very healthy improvement from around 3,500 to 5,000. It was alway strong from about 4,500, I'd say there is more power available now at 3,500 than there was at 4,500 and it climbs steeply and smoothly from 3,500.

3. I think there is improvement in the top end too. I'm expecting a few BHP peak increase. Its difficult to feel though, because the power band is now broader and smoother, feelings can be deceptive in such circumstances as a pronounced 'step' in power is often misconstrued as more power, rather than simply a step in power.

All in all, Sir Comnoz said he'd build me 'a street-able head' and that's most definitely what it is. It is noticeably stronger and more enjoyable to ride on the road now.

Not Dyno related, but very important in the real world, the 'Blue Bomber' is generally a first kick starter (albeit a very hefty kick being required) and it ticks over very reliably even after a sound thrashing.

I do not intend to play around any more with different velocity stacks on the Dyno. I'll run it with the stock 1 3/8 pipes and peashooters, with 1 1/2 pipes and peashooters, and with a Maney 2:1 system for comparisons.

@ Chris, you'll be pleased to hear that I'll send you the Maney system back straight afterwards (along with those valve gear parts we discussed), many thanks for the patient loan of this sir.

Until then Gentlemen...
 
Hi Eddie

No problem :D I will get my pistons machined one day :D
I now have everything else ready to rebuils the Mk4.

Chris
 
Hi Eddie.
Can hardly wait.
By then I hope I have been measured my short stroke too. The man who test the bike before have been sick and not at work lately.
 
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